don't exaclty know what a forum troll is. Maybe a person who views the forums alot? a person who posts alot in the forums? someone who disagrees with everything? or is it just an insult?
it tends to mean a very negative person, whether naturally or for their own amusements, who disagrees or disrupts something for their own amusement to create an argument or make someone feel bad.
I mean someone who intentionally causes mayhem online through controversy, to get replies from people. Trolls love to waste people's time by shocking them or pissing them off.
I found one interesting article about types of forum users, Flame Warriors. Don't know where I got it, maybe someone posted it here a while ago. Illustrated guide to guerilla forum warfare.
And to add to that, ignore, and then REPORT to a mod. And let them handle it from there. Trolling back to a troll is not good, it'll get YOU in trouble as well as the troll...